Fix version-pinning examples on /packages to match the repo-served version

[GuanzhouSong]

Summary

The version-pinning section on /packages shows 0.114-0 / 0.114.0-1.el9 as example output of apt-cache madison / dnf --showduplicates list, but the live APT/RPM repositories at documentdb.io currently serve 0.113-0 / 0.113.0-1.el9 (confirmed against the repo package indexes and documentdb.io/packages/release-info.json). Users following the pinning instructions would look for a version string the list commands never show.

• Split the single version constant into a latest-GitHub-release version (0.114-0, still used for the direct .deb/.rpm download filename examples, which correctly reference GitHub Release assets) and a repo-served version (0.113-0, now used for the pinning examples).
• Add a note that the package repositories can lag the newest GitHub release, so users should pin to a version the list command actually shows.

Also verified while auditing against released versions (no changes needed):

• The Debian 11 caveat is still accurate: a deb11 PG 18 package now exists in the APT repo, but it depends on postgresql-18-postgis-3, which bullseye-pgdg still does not ship, so it cannot install.
• The "no gateway package published" statements still hold for v0.114-0 (release assets are extension-only).
• The package catalog matrix matches the v0.114-0 release assets exactly.

Test plan

• tsc --noEmit passes
• eslint app/packages/page.tsx passes
• npm test — 102/102 pass